1. Field of the Invention
The present invention relates generally to a method and apparatus for disinfecting an enclosed space for the preservation and sterilization of harvested foods, vegetables, and flowers in a storage environment, and for reducing toxic gas levels associated with confining animals in an enclosed space, and more particularly to a method and apparatus for disinfecting an enclosed space by introducing a regulated ozone and oxygen gas mixture into the enclosed space.
2. Description of the Prior Art
One typical method for the preservation of harvested fruits, vegetables, and flowers on a large commercial scale is to store the product in an insulated room, or transport container such as an insulated trailer box with self-contained refrigeration (e.g. refrigerated trailer); a motor vehicle mounted insulated box with a self-contained or vehicle engine powered means of refrigeration; or with a detached insulated box with a self-contained means of refrigeration suitable for transport on a ship, barge, railroad car or over the road trailer (e.g. refrigerated cargo container) kept at low temperature, typically between 33.degree. fahrenheit and 45.degree. fahrenheit. In some of these refrigerated environments, the humidity may also be controlled, either by the removal or addition of moisture, to further preserve the appearance or freshness of the product. Some products, such as Vidalia sweet onions and all varieties of apples, can be kept in storage for longer periods than can be achieved by simple reduction in temperature. This longer term storage process is called controlled atmosphere storage and involves displacing of all but approximately 1% to 3% of the oxygen in the room with nitrogen and maintaining temperatures as close to freezing as can be achieved without actual freezing of the product.
These processes do extend the life of organic products such as vegetables, fruits, and flowers when compared to continued exposure of the fresh product to ambient temperatures. The principal purpose of the refrigerated room or transport container storage is to retard ripening by reducing the fresh products' generation of ethylene gas and to reduce the growth rate and product destroying abilities of opportunistic bacteria, fungus and molds. Because these storage and transport methods only retard and reduce natural processes, the term of storage is limited and variable depending on the temperature, humidity, and the population of plant pathogens contained in the storage and transport environment, as well as on the product itself.
The present invention provides an improved method and apparatus to enhance preservation and vegetable shelf life by sterilizing the ambient atmosphere in an enclosed space by introducing a regulated ozone and oxygen gas mixture into the enclosed space.
With respect to commercial food source animals, a typical method for housing animals on a large commercial scale in colder climates is to confine the animals to a building containing one or more rooms in which ventilation is controlled such that during the colder seasons there is not a lot of heat loss. Air exchange from outside to inside and vice versa is kept at a minimum to reduce energy consumption and to avoid chilling the animals, particularly the very young. Conversely, in hot climates, it necessary to cool the facility to avoid heat stressing the animals. Air exchange is reduced to a minimum to reduce energy costs for cooling. This reduction in the introduction of fresh air containing healthful levels of oxygen and some amounts of naturally occurring ozone is deleterious to the health of the animals. The lowered oxygen levels and the increase in toxic gases (ammonia, methane, and hydrogen sulphide being the principal gases) places a greater strain on the animals' kidneys due to the increased presence of toxins in the blood and is detrimental to the animals' respiratory system as elevated ammonia level is a mucus membrane irritant. Another affect of the reduced air exchange is a raising of the humidity level. Many fungus and bacteria are dormant at lower humidity levels and these become much more active as the relative humidity increases above 60%.
The present invention can continuously provide an oxygen and ozone injected treatment for the animal ambient air to improve energy efficiency while reducing toxins.
Thus the ozone and oxygen system of the present invention can be used for preserving the shelf life of produce such as vegetables and for improving the ambient air and energy efficiency for enclosed animals.
The present invention relates to a method and apparatus for treating ambient gases in an enclosed space with ozone and oxygen. During storage, the process of respiration of fruit is speeded up and so is ripening. Ethylene is produced which affects other fruit and so initiates even more intensive ripening. The external signs of this process are browning of the skin, softening of the flesh of the fruit and, finally, decay. Ozone gas (O.sub.3), which is an allotrope of oxygen (O.sub.2), can be used to extend the term of storage because it oxidizes the ethylene gas in the atmosphere of the storage environment and is lethal to bacteria, fungus, and molds. However, excessive concentrations of ozone can damage a product by oxidizing sugars and altering flavor, altering the metabolism of cut flowers thereby causing them to wilt, and accelerating other natural plant activity such as sprouting in bulb crops such as onions. Because there is no oxygen in a controlled atmosphere storage process, ozone must be manufactured from oxygen obtained from outside the storage environment. Ozone manufactured from ambient air, whether that contained within the storage room or introduced from outside, contains nitrous oxides and nitric acid that can affect flavor and cause discoloration of the product. Further damage can be caused to the storage room itself from acidic attack of the structural and operating components.
The introduction of a high purity oxygen and ozone mixture (e.g. 4%-7% O.sub.3) into the storage environment significantly reduces ethylene gas levels by oxidation. Ethylene is broken down into water vapor and carbon dioxide. By maintaining a residual amount of ozone of 0.02 to 0.04 parts per million by weight in the air in the room after available ozone is consumed by reaction with the gases, the bacteria, fungus, and molds in the air and on surfaces are continuously suppressed. Additionally, this concentration of ozone is less than the 0.05 parts per million limit for human exposure in effect in Canada, Europe, and Japan, and the 0.1 parts per million limit in effect in the United States of America. This permits workers to move in an out of the ozonated area without hazard. Further, pathogens transported into the storage environment by humans are quickly suppressed.
Prior to the introduction of products into the storage or transport environment and in the absence of humans, the high purity oxygen and ozone mixture can be elevated to very much higher levels with no upper limit control in order to decontaminate and deodorize the storage or transport environment. This is particularly useful when the environment has been used to transport other products which may have rotted and released excessive levels of ethylene gas and plant pathogens. In other instances, such as the seasonal or the intermittent use of storage or transport, the refrigeration may have been interrupted and outside air introduced through openings. Bacteria, fungus, and mold colonies will have bloomed and will be at their peak. Furthermore, ozone eliminates or reduces mold build-up on cooling coils. Dirt and dust build-up is reduced, drastically reducing the number of times the cooling coils need cleaning and increasing energy efficiency. Some storage environments, particularly cargo containers, may have been previously used for refrigerated transport of other food stuffs, such as fish that leave a strong residual odor. As is well known, ozone is unmatched as a deodorizer. However, to totally eliminate "heavy" odors, higher concentrations (e.g. 0.1 p.p.m.) of ozone are required to react with gases in the air and odors trapped in materials. Ozone at a concentration of 0.1 p.p.m. will destroy microorganisms and eliminate most odors within 48 hours.